For over thirty years, ion engines have been proposed for propulsion of vehicles in space. Outside of space propulsion, ion generation may also be applied to various types of materials processing systems involving ion sources, such as for ion beam etching or micromachining. Ion engines use movement of ions to provide thrust.
Generally, an ion engine has an ion accelerator system that uses an anode, a cathode, a screen grid and an accelerator grid coupled within a thruster housing. Generally, an ion engine works by generating an inert gas plasma within the thruster housing. Xenon is an example of a suitable gas. A charge within the plasma between the anode and cathode forms ions. The inert gas ions leave the thruster through the charged screen and accelerator. The net force from the ions leaving the thruster housing generates a thrust. A neutralizer is located outside the thruster housing and generates electrons. The electrons are attracted to the ions so the ions do not re-enter the thruster housing as they otherwise would in space.
A number of power supplies are used to power the various components of the system. Heaters, the accelerator, the screen, the anode and cathode of the thruster, and the anode and cathode of the neutralizer each have separate power supplies. The power supply for the screen processes a majority of the power of the spacecraft. A wide extreme of power and voltage supplied by the spacecraft bus varies significantly. Particularly as a spacecraft moves further from the sun, the amount of load also varies. The ratio of the output to input voltage may be as high as 4:1.
Various other known designs for supplying power over a wide dynamic performance range include using a single stage high-power inverter designed for the worst case voltage and power conditions. A single stage design has a minimum number of parts and good efficiency when operating near the maximum design point. However, when the system does not operate near its design point, thermal stresses are created due to the heat dissipation that is concentrated in a few large components requiring massive heat sinks. High stress levels on the semi-conductors for voltage, current and temperature work against reliability for single stage power processing. As the power level is decreased away from the design point, efficiency drops.
It is therefore an object of the invention to provide a power supply system that operates reliably over a wide dynamic range of performance while maintaining good efficiency over the dynamic range.